@Mark_O: First, sorry for the irony of the replies above.
I believe in his observation too, and of course, it is no coincidence. I can't understand why I got these results.
But once that I found the min time between pulses that allowed the second trigger, I run the test several times, increasing the time between pulses slightly, until that always the second trigger was produced.
So, if this test was correct, then wfrm/s are limited, but this is absurd.
Note_1: The test was done with the previous firmware version, and seems that there is some relation between wfrm/s and re-arm time, ie if one increases the other also, and vice versa.
Note_2: I no longer have the DS2000, to make this test with new firmware version. But if someone repeats this test would be better if the results will be published in this topic:
"REVIEW - Rigol DS2072 - First Impressions of the DS2000 series from Rigol".